Multilayer films for optimized soft underlayer magnetic properties of dual layer perpendicular recording media

ABSTRACT

A perpendicular magnetic recording medium includes a hard magnetic recording layer and a soft magnetic underlayer adjacent the hard magnetic recording layer. The soft magnetic underlayer includes first and second ferromagnetically coupled multilayer structures and a coupling layer positioned between the first and second multilayer structures for antiferromagnetically coupling the first and second multilayer structures. A magnetic disc drive storage system incorporating such a perpendicular magnetic recording medium and a method of making such a perpendicular magnetic recording medium are also included.

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of U.S. ProvisionalApplication No. 60/312,173 filed Aug. 14, 2001.

FIELD OF THE INVENTION

[0002] The invention relates to perpendicular magnetic recording media,and more particularly, relates to a soft magnetic underlayer of suchmedia.

BACKGROUND OF THE INVENTION

[0003] Perpendicular magnetic recording systems have been developed foruse in computer hard disc drives. A typical perpendicular recording headincludes a trailing write pole, a leading return or opposing polemagnetically coupled to the write pole, and an electrically conductivemagnetizing coil surrounding the yoke of the write pole. Perpendicularrecording media may include a hard magnetic recording layer withvertically oriented magnetic domains and a soft magnetic underlayer toenhance the recording head fields and provide a flux path from thetrailing write pole to the leading or opposing pole of the writer. Suchperpendicular recording media may also include a thin interlayer betweenthe hard recording layer and the soft underlayer to prevent exchangecoupling between the hard and soft layers.

[0004] To write to the magnetic recording medium, the recording head isseparated from the magnetic recording medium by a distance known as theflying height. The magnetic recording medium is moved past the recordinghead so that the recording head follows the tracks of the magneticrecording medium, with the magnetic recording medium first passing underthe opposing pole and then passing under the write pole. Current ispassed through the coil to create magnetic flux within the write pole.The magnetic flux passes from the write pole tip, through the hardmagnetic recording track, into the soft underlayer, and across to theopposing pole.

[0005] In addition, the soft underlayer helps during the read operation.During the read back process, the soft underlayer produces the image ofmagnetic charges in the magnetically hard layer, effectively increasingthe magnetic flux coming from the medium. This provides a higherplayback signal.

[0006] Perpendicular recording designs have the potential to supportmuch higher linear densities than conventional longitudinal designs dueto a reduced demagnetizing field in the recording transitions. Inaddition, the described bilayer medium is used in perpendicularrecording to allow increased efficiency of the recording head. The softmagnetic underlayer of the perpendicular recording medium forms inverseimage charges and substantially magnifies both the write field duringrecording and the fringing field of the recorded transition duringreproduction. The quality of the image, and therefore the effectivenessof the soft underlayer, depends upon the permeability of the softunderlayer.

[0007] To support the high image efficiency, the soft underlayer shouldbe in an unsaturated state. However, during recording a top portion ofthe soft underlayer is likely to be saturated. Therefore, thickness andmagnetic saturation induction, B_(s), of the soft underlayer needs to bematched to appropriate parameters of the recording head. Magneticsaturation of the soft underlayer causing the permeability reductionwill result in write field degradation. Therefore, the soft underlayershould be relatively thick and have a high magnetic saturationinduction, e.g. B_(s)>1 Tesla.

[0008] However, one of the challenges of implementing perpendicularrecording is to resolve the problem of soft underlayer noise. The noisemay be caused by fringing fields generated by magnetic domains, oruncompensated magnetic charges, in the soft underlayer that can besensed by the reader. For example, soft underlayer materials, such asNi₈₀Fe₂₀ or Co₉₀Fe₁₀, may exhibit multi-domain states that produce noiseenhancement in the read-back signals, hence, degrading thesignal-to-noise (SNR) ratio. If the magnetic domain distribution of suchmaterials is not carefully controlled, very large fringing fields canintroduce substantial amounts of noise in the read element. Not only canthe reader sense the steady state distribution of magnetization in thesoft underlayer, but it can also affect the distribution ofmagnetization in the soft underlayer, thus generating time dependentnoise. Both types of noise should be minimized.

[0009] In addition, magnetostatic interaction between the softunderlayer and the hard layer can degrade SNR ratio and reduce lineardensity.

[0010] There is identified a need for perpendicular magnetic recordingmedia with a soft magnetic underlayer that overcomes limitations,disadvantages, or shortcomings of known perpendicular magnetic recordingmedia.

SUMMARY OF THE INVENTION

[0011] The invention meets the identified need, as well as other needs,as will be more fully understood following a review of thisspecification and drawings.

[0012] In accordance with an aspect of the invention, a perpendicularmagnetic recording medium comprises a hard magnetic recording layer anda soft magnetic underlayer under the hard magnetic recording layer. Thesoft magnetic underlayer comprises a first ferromagnetically coupledmultilayer structure and a second ferromagnetically coupled multilayerstructure. The soft underlayer also includes a coupling layer that ispositioned between the first and second multilayer structures forantiferromagnetically coupling the multilayer structures to one another.Each multilayer structure may include first and second magnetic layersthat are ferromagnetically coupled by an interlayer positionedtherebetween. Each multilayer structure may include additional magneticlayers with interlayers positioned therebetween.

[0013] In accordance with yet another aspect of the invention, amagnetic disc drive storage system comprises a housing, a perpendicularmagnetic recording medium positioned in the housing and a movablerecording head mounted in the housing adjacent the perpendicularmagnetic recording medium. The perpendicular magnetic recording mediumcomprises a hard magnetic recording layer and a soft magnetic underlayerunder the hard magnetic recording layer. The soft magnetic underlayerincludes a first ferromagnetically coupled multilayer structure, asecond ferromagnetically coupled multilayer structure, and a couplinglayer positioned therebetween for antiferromagnetically coupling thefirst and second ferromagnetically coupled multilayer structures.

[0014] In accordance with another aspect of the invention, aperpendicular magnetic recording medium comprises a hard magneticrecording layer and a soft magnetic layer under the hard magneticrecording layer. The soft magnetic underlayer includes a plurality ofmagnetic layers and a plurality of interlayers individually interposedbetween each of the plurality of magnetic layers in order toantiferromagnetically couple each of the plurality of magnetic layerssuccessively.

[0015] In accordance with a further aspect of the invention, a method ofmaking a laminated magnetically soft underlayer of a perpendicularmagnetic recording medium is provided. The method includes depositing afirst ferromagnetically coupled multilayer structure on a substrate. Themethod also includes depositing a coupling layer on the firstferromagnetically coupled multilayer structure. The method also includesdepositing a second ferromagnetically coupled multilayer structure onthe coupling layer, wherein the coupling layer serves toantiferromagnetically couple the first and second multilayer structures.The step of depositing the first ferromagnetically coupled multilayerstructure on a substrate may include depositing an interlayer on thesubstrate, depositing a magnetic layer on the interlayer, depositing anadditional interlayer on the magnetic layer, and depositing anadditional magnetic layer on the additional interlayer. The step ofdepositing a second multilayer structure on the coupling layer mayinclude depositing a magnetic layer on the coupling layer, depositing aninterlayer on the magnetic layer, depositing an additional magneticlayer on the interlayer, and depositing an additional interlayer on theadditional magnetic layer.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016]FIG. 1 is a pictorial representation of a disc drive that mayutilize a perpendicular recording medium in accordance with theinvention.

[0017]FIG. 2 is a partially schematic side view of a perpendicularmagnetic recording head and a perpendicular recording magnetic medium inaccordance with the invention.

[0018]FIG. 3 is an embodiment of a soft magnetic underlayer of theinvention.

[0019]FIG. 4 illustrates a B-H curve of the soft magnetic underlayerillustrated in FIG. 3.

[0020]FIG. 5 illustrates an additional embodiment of a soft magneticunderlayer of the invention.

[0021]FIG. 6 illustrates a B-H curve of the soft magnetic underlayerillustrated in FIG. 5.

[0022]FIG. 7 is a schematic of a glass disc with hard magnetic layer,interlayer, and soft magnetic underlayer and a magnetic force microscopytip.

[0023]FIG. 8 is a magnetic force microscopy (MFM) image of an AC erasedhard layer on a ceramic glass substrate.

[0024]FIG. 9a is an MFM image of a soft magnetic underlayer spaced apartfrom an AC erased vertically oriented hard layer medium by a Ta layerwith a thickness of approximately 5 nm, where the soft layer illustratedin FIG. 9a includes a Permalloy (NiFe) film with a thickness of 200 nm.

[0025]FIG. 9b is an MFM image of a soft magnetic underlayer spaced apartfrom an AC erased vertically oriented hard layer medium by a Ta layerwith a thickness of approximately 5 nm, where the soft layer includes(Ni₈₀Fe₂₀ 20 nm/Ru 1.5 nm)×5/Ru 0.5 nm/(Ni₈₀Fe₂₀ 20 nm/Ru 1.5 nm)×5.

[0026]FIG. 10 compares spin stand test noise results for a single filmof Permalloy with a thickness of 200 nm and a multilayer film of NiFe/Ruconstructed in accordance with the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0027] The invention provides a perpendicular recording medium withferromagnetic and antiferromagnetic coupling in a soft magneticunderlayer of the perpendicular recording medium. The invention isparticularly suitable for use with a magnetic disc storage system. Arecording head, as used herein, is defined as a head capable ofperforming read and/or write operations. Antiferromagnetic coupling, asused herein, generally refers to the coupling between ferromagneticlayers or multilayer structures such that adjacent ferromagnetic layersor multilayer structures have magnetizations that point in generallyopposite directions. Ferromagnetic coupling, as used herein, generallyrefers to indirect coupling between ferromagnetic layers or multilayerstructures such that adjacent ferromagnetic layers or multilayerstructures have magnetizations that point in generally the samedirections.

[0028]FIG. 1 is a pictorial representation of a disc drive 10 that canutilize a perpendicular recording medium in accordance with thisinvention. The disc drive 10 includes a housing 12 (with the upperportion removed and the lower portion visible in this view) sized andconfigured to contain the various components of the disc drive. The discdrive 10 includes a spindle motor 14 for rotating at least one magneticstorage medium 16, which may be a perpendicular magnetic recordingmedium, within the housing, in this case a magnetic disc. At least onearm 18 is contained within the housing 12, with each arm 18 having afirst end 20 with a recording head or slider 22, and a second end 24pivotally mounted on a shaft by a bearing 26. An actuator motor 28 islocated at the arm's second end 24 for pivoting the arm 18 to positionthe recording head 22 over a desired sector or track of the disc 16. Theactuator motor 28 is regulated by a controller, which is not shown inthis view and is well known in the art.

[0029]FIG. 2 is a partially schematic side view of a perpendicularmagnetic recording head 22 and a perpendicular recording magnetic medium16. The recording head 22 is well known in the art and includes a writersection comprising a trailing main pole 30 and a return or opposing pole32. A magnetizing coil 33 surrounds a yoke 35, which connects the mainpole 30 and return pole 32. The recording head 22 also includes a readersection comprising a read element 34 positioned between a reader pole 36and the opposing pole 32. The read element 34 may be a conventional GMRreader, MR reader, inductive reader, or the like. In the embodimentshown in FIG. 2, the reader section shares the opposing pole 32 of thewriter section.

[0030] Still referring to FIG. 2, the perpendicular magnetic recordingmedium 16 is positioned under the recording head 22. The recordingmedium 16 travels in the direction of arrow A during recording. Therecording medium 16 includes a substrate 38, which may be made of anysuitable material such as ceramic glass, amorphous glass, or NiP platedAlMg. A soft magnetic underlayer 40 is deposited on the substrate 38.The soft magnetic underlayer, in accordance with the invention, is alaminated soft magnetic underlayer, which will be described in detailherein. A spacer layer 39 may be deposited on the soft magneticunderlayer 40. The spacer layer 39 may be made of any suitable materialsuch as, for example, Cr, Ti, Ta, Ru or TiO₂. In addition, the spacerlayer 39 may have a thickness from about 5 to about 50 angstroms. A hardmagnetic recording layer 41, which in this invention is a perpendicularrecording layer, is deposited on the spacer layer 39. Suitable hardmagnetic materials for the hard magnetic recording layer 41 may include,for example, CoCr, FePd, FePt, CoPd, CoFePd, CoCrPt, or CoCrPd. The hardmagnetic layer 41 may have a thickness from about 2 nm to about 40 nm. Aprotective overcoat 47, such as a diamond-like carbon, may be appliedover the hard magnetic recording layer 41.

[0031] Referring to FIG. 3, the soft magnetic underlayer 40 is shown inmore detail. The soft magnetic underlayer 40 includes a firstferromagnetically coupled multilayer structure 42 and a secondferromagnetically coupled multilayer structure 44. A coupling layer 46is positioned between the first and second multilayer structures 42 and44. The coupling layer 46 antiferromagnetically couples the first andsecond multilayer structures 42 and 44. In accordance with theinvention, and as described herein, the soft magnetic underlayer 40results in a reduction of noise in the soft magnetic underlayer 40 and,hence, an improved signal to noise ratio (SNR). This is achieved by thecreation of a primarily single domain state within the first multilayerstructure 42 (as designated by arrows 43) and within the secondmultilayer structure 44 (as designated by arrows 45), as well as, thecreation of a generally zero net remanant magnetic moment that resultsfrom the first multilayer structure 42 being antiferromagneticallycoupled by the coupling layer 46 to the second multilayer structure 44.

[0032] The first ferromagnetically coupled multilayer structure 42includes a plurality of magnetic layers 48 that are ferromagneticallycoupled by a plurality of interlayers 50 positioned therebetween.Similarly, the second ferromagnetically coupled multilayer structure 44includes a plurality of magnetic layers 52 that are ferromagneticallycoupled by a plurality of interlayers 54 positioned therebetween.Selection of various parameters such as, for example, the materialselection and material thickness for the magnetic layers 48 and theinterlayers 50 results in the ferromagnetic coupling of the magneticlayers 48 to form the first ferromagnetically coupled multilayerstructure 42. Similarly, various parameters such as, for example,material selection and material thickness of the magnetic layers 52 andthe interlayers 54 results in the ferromagnetic coupling of the magneticlayers 52 for the formation of the second ferromagnetically coupledmultilayer structure 44. The various parameters, such as, materialselection and thickness thereof, along with the number of magneticlayers 48 and 52 and the number of interlayers 50 and 54, determine thedegree of ferromagnetic coupling within each of first and secondmultilayer structures 42 and 44, respectively.

[0033] In addition, various parameters of the coupling layer 46 such as,for example, material selection and thickness thereof, control thedegree of antiferromagnetic coupling between the first and secondmultilayer structures 42 and 44.

[0034] The magnetic layers 48 and 52 may comprise, for example,Permalloy, any binary or ternary alloy of Co, Fe, Ni or a Ni—Fe—Co—Xalloy wherein X equals any alloying material suitable for microstructurecontrol such as, for example, Ru, Cr, Cu, Au, Al, or Re etc. However, itwill be appreciated that these materials are illustrative of materialssuitable for use with the invention but other suitable materials may beused. The magnetic layers 48 and 52 may each have a thickness of fromabout 10 nm to about 50 nm.

[0035] The interlayers 50 and 54 may comprise, for example, Ru, Cr, Cu,Al₂O₃, Re, Au, or Al. However, it will be appreciated that thesematerials are illustrative of materials suitable for use with theinvention but other suitable materials may be used. The interlayers 50and 54 may each have a thickness from about 0.5 nm to about 5 nm.

[0036] The coupling layer 46 may include, for example, Ru, Cr, Cu, Al₂O₃or Re. However, it will be appreciated that these materials areillustrative of materials suitable for use with the invention but othersuitable materials may be used. The coupling layer 46 may have athickness of from about 0.5 nm to about 5.0 nm.

[0037] In accordance with the invention, the soft underlayer 40, andparticularly the first and second multilayer structures 42 and 44,exhibit many suitable properties for forming a soft underlayer. Forexample, they exhibit a ratio of saturation magnetization to saturationmagnetic field that is tunable, primarily because the latter is afunction of the interlayer 50 and 54 thicknesses and of the bandstructure matching between the layers 48 and 52 and the interlayers 50and 54. Advantageously, this allows for optimization of side readingand/or writing and enhancement of the SNR. Another advantage is that themultilayer structures 42 and 44 of the soft underlayer 40 can exhibit aprimarily single domain state. In addition, the soft underlayer 40 canexhibit reduced magnetostatic interaction with the hard magneticrecording layer 44, therefore, having magnetic properties that areindependent of the recording signals. The parameters of the softunderlayer 40 and the multilayer configuration that make up the softunderlayer 40 that can be varied to reduce the magnetostatic interactionwith the hard magnetic recording layer 44 to reduce noise levels, and tooptimize the writing and reading processes are, for example, thethicknesses of the ferromagnetic layers 48 and 52 and the interlayers 50and 54 and the thickness of the coupling layer 46. In addition, thematerial selection for the layers 48 and 52, the interlayers 50 and 54,and the coupling layer 46 may be varied in accordance with the inventionto achieve the desired results. Other parameters that may be variedinclude the number and combination of the magnetic layers 48 and 52 andthe interlayers 50 and 54, the ferromagnetic layer saturationmagnetization, 4 π M_(s), and the ratio of 4 π M_(s)/H_(s).

[0038]FIG. 4 illustrates the B-H curves of a multilayer stackconstructed in accordance with the invention to form the soft magneticunderlayer 40. Specifically, the soft underlayer 40 may be constructedas follows: (Ni₈₀Fe₂₀ 20 nm/Ru 1.5 nm)×5/Ru 0.5 nm/(Ni₈₀Fe₂₀ 20 nm/Ru1.5 nm)×5. The layers Ni₈₀Fe₂₀ 20 nm/Ru 1.5 nm/Ni₈₀Fe₂₀ 20 nm, whichcorresponds, for example, to magnetic layer 48/interlayer 50/magneticlayer 48, are ferromagnetically coupled through RKKY interaction. Thelayers Ni₈₀Fe₂₀ 20 nm/Ru 0.5 nm/Ni₈₀Fe₂₀ 20 nm, which corresponds, forexample, to magnetic layer 48/coupling layer 46/magnetic layer 52, areantiferromagnetically coupled through RKKY interaction. FIG. 4illustrates that the described soft underlayer structure 40 has a nearzero net remanent magnetic moment due to an antiparallel magneticconfiguration between the magnetic layers 48 and between the magneticlayers 52 that form the first and second multilayers structures 42 and44 respectively. Moreover, the magnetization curves indicate very smallhysteresis, in accordance with the fact that a single-domain state wasstabilized.

[0039]FIG. 5 illustrates another embodiment of the invention. In thisembodiment, adjacent magnetic layers are antiferromagnetically coupledthroughout the film thickness. Specifically, the embodiment includes asoft magnetic underlayer 240 that may serve in place of, for example,the soft magnetic underlayer 40 as described herein. The soft underlayer240 includes a plurality of magnetic layers, such as magnetic layers248, and a plurality of interlayers, such as interlayers 250, that areinterposed between the magnetic layers 248. The interlayers 250antiferromagnetically couple each successive pair of magnetic layers248. Similar to the description set forth herein regarding theadvantages and varying of parameters for the soft underlayers 40 and140, the soft underlayer 240, and specifically the magnetic layers 248and interlayers 250, may be similarly arranged. For example, to providefor the desired antiferromagnetic coupling between the magnetic layers248, the material and thickness thereof for the magnetic layers 248 andinterlayers 250 may be varied to reduce, for example, magnetostaticinteraction with the hard magnetic recording layer, such as hardrecording layer 44, reduce noise and optimize the writing and readingprocesses.

[0040]FIG. 6 illustrates the B-H curves of a multilayer stackconstructed in accordance with the invention to form the soft magneticunderlayer 240, as illustrated in FIG. 5. Specifically, the softunderlayer 240 may be constructed as follows: (Ni₈₀Fe₂₀ 50 nm/Ru 0.6nm)×4. This structure corresponds, for example, to (magnetic layer248/interlayer 250)×4, which are antiferromagnetically coupled. FIG. 6illustrates that the described soft underlayer structure 240 has a nearzero net remanent magnetic moment due to an antiparallel magneticconfiguration between the magnetic layers 248 and the interlayers 250.

[0041] To illustrate the invention, comparative investigations wereperformed between a single layer film formed of, for example, PermalloyNi₈₀Fe₂₀, and a multilayer structure formed of, for example, Ni₈₀Fe₂₀/Rumultilayers. Aspects illustrated by the experimental investigation, aswill be described herein, were carried out using magnetization andanisotropic magnetoresistance measurements, magnetic force microscopy(MFM) and spin stand tests.

[0042] Referring to FIGS. 7, 8, 9 a and 9 b, a multilayer structurewith, for example, the physical structure similar to that previouslydescribed in FIG. 3 to form the soft underlayer is compared to a singlelayer film of Permalloy (Ni₈₀Fe₂₀) with a thickness of 200 nm. Both themultilayer structure and the single layer film were deposited on thestructure: Ta 5 nm/(CoCr/Pd)×N/Ta/glass ceramic disc substrate, withN=16.

[0043]FIG. 7 illustrates a schematic of a ceramic glass disc substrate238 with a hard layer 241, interlayer 239, and soft underlayer 240 suchas those prepared for MFM imaging using an MFM tip 260. A hard magneticfilm, e.g. hard layer 241, with perpendicular anisotropy and highlyexchanged coupled grains, characterized by a nucleation fieldapproximately equal to a coercive force with a value of 4.5 kOe and asquareness=1, was AC erased with a Kerr-polar looper. An MFM imaging ofthe AC erased layer on a ceramic glass substrate is presented in FIG. 8.The AC erased film with perpendicular anisotropy shows large magneticclusters having up and down magnetic distributions (as represented bythe relatively large areas of light and dark regions or magneticcontrast shown in FIG. 8) such that only local fields are present butthe net magnetic field is zero.

[0044] Soft underlayers were then deposited on the AC erased media andthe magnetic states were imaged by MFM. While single films of Permalloyexhibited multidomain states (as represented by the variation ofmagnetic contrast shown in FIG. 9a), the antiferromagnetically coupledmultilayers exhibited a considerably lower density of domain walls (asrepresented by the reduced or more uniform magnetic contrast shown inFIG. 9b as compared to FIG. 9a) as shown by the MFM images presented inFIGS. 9a and 9 b. Specifically, FIGS. 9a and 9 b illustrate MFM imagesof soft layers, spaced apart from an AC erased vertically oriented hardlayer medium by a Ta layer with a thickness of approximately 5 nm,wherein FIG. 9a has a soft layer of Ni₈₀Fe₂₀ ₂₀ 200 nm and FIG. 9b has asoft layer of (Ni₈₀Fe₂₀ 20 nm/Ru 1.5 nm)×5/Ru 0.5 nm/(Ni₈₀Fe₂₀ 20 nm/Ru1.5 nm)×5.

[0045]FIG. 10 compares spin stand test results of AC erased noise as afunction of the frequency on dual layer perpendicular media discs, usingeach a single layer of NiFe and a NiFe/Ru multilayer film. Specifically,the tests were carried out with a dual layer perpendicular media onceramic glass discs, using each a hard layer of (Co, Cr/Pd)×N, separatedby 10 nm of Ta from a soft underlayer of Ni₈₀Fe₂₀ 200 nm and of(Ni₈₀Fe₂₀ 20 nm/Ru 1.5 nm)×5/Ru 0.5 nm/(Ni₈₀Fe₂₀ 20 nm/Ru 1.5 nm)×5. Theexperimental values of AC erased noise, obtained with a spin stand test,as illustrated, correlate with the results obtained by MFM. The duallayer disc that used a soft underlayer consisting of NiFe/Ru multilayerfilm exhibited considerably lower noise than that using a single layerof Permalloy.

[0046] The invention also includes a method of making a magneticallysoft underlayer of a perpendicular magnetic recording medium. Forexample, a method for making the soft underlayer 40 (shown in FIG. 3)includes depositing a first ferromagnetically coupled multilayerstructure, such as multilayer structure 44, on a substrate. The methodalso includes depositing a coupling layer 46 on the multilayer structure44 and depositing an additional ferromagetically coupled multilayerstructure such as multilayer structure 42, on the coupling layer 46.This results in a soft underlayer where the coupling layer 46antiferromagnetically couples the multilayer structures 42 and 44.

[0047] More specifically, the depositing of the multilayer structurelayer 44 on the substrate may include depositing an interlayer, such asinterlayer 54, on the substrate followed by depositing a magnetic layer,such as magnetic layer 52, on the interlayer 54. Additional magneticlayers and interlayers may be deposited to form the multilayer structure44. In addition, the depositing of the multilayer structure 42 on thecoupling layer 46 may include depositing a magnetic layer, such asmagnetic layer 48, on the coupling layer 46 and depositing aninterlayer, such as interlayer 50, on the magnetic layer 48. Additionalmagnetic layers and interlayers may also be deposited thereon to formthe multilayer structure 42. In order to obtain the describedantiferromagnetically coupled multilayer structures with suitableproperties that provide, for example, reduced noise and optimize readingand writing as described herein, the multilayer structures 42 and 44,and more specifically the magnetic layers 48 and 52, interlayers 50 and54, and coupling layer 46, may vary the materials and thicknesses asdescribed herein in various arrangements.

[0048] The depositing of layers may be done using, for example, ion-beamor sputtering or other known deposition techniques.

[0049] Whereas particular embodiments of the invention have beendescribed herein for the purpose of illustrating the invention and notfor purpose of limiting the same, it will be appreciated by those ofordinary skill in the art that numerous variations of the details,materials, and arrangements of parts may be made within the principleand scope of the invention without departing from the invention asdescribed herein and in the appended claims.

What is claimed is:
 1. A perpendicular magnetic recording medium,comprising: a hard magnetic recording layer; and a soft magneticunderlayer under the hard magnetic recording layer, wherein the softmagnetic underlayer comprises: a first ferromagnetically coupledmultilayer structure; a second ferromagnetically coupled multilayerstructure; and a coupling layer positioned between said first and secondferromagnetically coupled multilayer structures, said coupling layerantiferromagnetically coupling said first and second ferromagneticallycoupled multilayer structures.
 2. The recording medium of claim 1,wherein said first ferromagnetically coupled multilayer structureincludes first and second magnetic layers that are ferromagneticallycoupled by an interlayer positioned therebetween.
 3. The recordingmedium of claim 2, wherein said first and second magnetic layers eachhave a thickness of from about 10 nm to about 50 nm.
 4. The recordingmedium of claim 2, wherein said interlayer comprises at least onematerial selected from Ru, Cr, Cu, Al₂O₃, Re, Au, and Al.
 5. Therecording medium of claim 2, wherein said interlayer has a thickness offrom about 0.5 nm to about 5 nm.
 6. The recording medium of claim 2,wherein said first ferromagnetically coupled multilayer structureincludes a third magnetic layer that is ferromagnetically coupled by anadditional interlayer to said second magnetic layer.
 7. The recordingmedium of claim 1, wherein said coupling layer comprises at least onematerial selected from Ru, Cr, Cu, Al₂O₃ and Re.
 8. The recording mediumof claim 1, wherein said coupling layer has a thickness of from about0.5 nm to about 5.0 nm.
 9. The recording medium of claim 1, wherein saidsecond ferromagnetically coupled multilayer structure includes first andsecond magnetic layers that are ferromagnetically coupled by aninterlayer positioned therebetween.
 10. The recording medium of claim 9,wherein said first and second magnetic layers each have a thickness offrom about 10 nm to about 50 nm.
 11. The recording medium of claim 9,wherein said interlayer comprises at least one material selected fromRu, Cr, Cu, Al₂O₃, Re, Au and Al.
 12. The recording medium of claim 8,wherein said interlayer has a thickness of from about 0.5 nm to about 5nm.
 13. The recording medium of claim 9, wherein said secondferromagnetically coupled multilayer structure includes a third magneticlayer that is ferromagnetically coupled by an additional interlayer tosaid second magnetic layer.
 14. A magnetic disc drive storage system,comprising: a housing; a perpendicular magnetic recording mediumpositioned in said housing; a movable recording head mounted in saidhousing adjacent said perpendicular magnetic recording medium; and saidperpendicular magnetic recording medium comprising a hard magneticrecording layer and a soft magnetic underlayer under the hard magneticrecording layer, wherein the soft magnetic underlayer comprises: a firstferromagnetically coupled multilayer structure; a secondferromagnetically coupled multilayer structure; and a coupling layerpositioned between said first and second ferromagnetically coupledmultilayer structures, said coupling layer antiferromagneticallycoupling said first and second ferromagnetically coupled multilayerstructures.
 15. A perpendicular magnetic recording medium, comprising: ahard magnetic recording layer; and a soft magnetic underlayer under thehard magnetic recording layer, wherein the soft magnetic underlayercomprises: a plurality of magnetic layers; and a plurality ofinterlayers individually interposed between each of said plurality ofmagnetic layers to antiferromagnetically couple each of said pluralityof magnetic layers successively.
 16. A method of making a laminatedmagnetically soft underlayer of a perpendicular magnetic recordingmedium, comprising: depositing a first ferromagnetically coupledmultilayer structure on a substrate; depositing a coupling layer on saidfirst ferromagnetically coupled multilayer structure; and depositing asecond ferromagnetically coupled multilayer structure on said couplinglayer, wherein said coupling layer antiferromagnetically couples saidfirst and second ferromagnetically coupled multilayer structures. 17.The method of claim 16, wherein said step of depositing a firstferromagnetically coupled multilayer structure on the substratecomprises; depositing an interlayer on the substrate; depositing amagnetic layer on the interlayer; depositing an additional interlayer onthe magnetic layer; and depositing an additional magnetic layer on theadditional interlayer.
 18. The method of claim 17, including forming themagnetic layer and additional magnetic layer to each have a thickness offrom about 10 nm to about 50 nm.
 19. The method of claim 16, whereinsaid step of depositing a second ferromagnetically coupled multilayerstructure on the coupling layer comprises; depositing a magnetic layeron the coupling layer; depositing an interlayer on the magnetic layer;depositing an additional magnetic layer on the interlayer; anddepositing an additional interlayer on the additional magnetic layer.20. The method of claim 19, including forming the magnetic layer andadditional magnetic layer to each have a thickness of from about 10 nmto about 50 nm.